Moving target indication apparatus



Patented Jan. 26, 1954 2,667,634

2,667,634 Movma TARGETI'N'DICATION. errermrrrs:

Geolfrey Walter Hart,v Stoke-.1 Poges. England,.. asa signer to Electric & MusicalIndnstricsLim. ited, Hayes, gland, a company of- Great Britain Application-November 10, 1948; Seria-INo; 59,309

Claims priority, application; Great Britain, November 15,1941

2 Claims. 34'3-7-.'7)

This invention relates to radiolocation appara Figure. 2 represents. a. 153., P. I. display obtained tus of th well-known, type incorporating a plan WithQllt the. employment. of the invention, position indicator for providing a display indicat- Figure 3represents a transparency, and ing the positions of objects in a field explored- Figure a representsaP HI; displayobtained by means of a rotating'or swinging antenna. In 5 when. the transparency cf, Figure 3 is employed. many uses of apparatus of thistype it is required Referring to the drawing reference numeral i only to discern some objects, for example moving indicates the cathode ray tube of a P. P. I. appaor movable objects, or to distinguish such objects ratus. The details of' construction of said apreadily from some other obj'ects,,for example fixed paratus willbe. understood by those familiar with objects. For example, the apparatus may be used the art, and the apparatus will. accordingly be on an airfield for the purpose of detecting. the described only to, the extent necessary for expresence or position of aircraft, motor vehicles plainingthepresentinvention Around the neck or the like movable objects on the airfield. Howof the cathode ray tube, l is mounted; a carrier ever, fixed objects, for example hangars and of- 2 on which are mount'edldeflection. 0, car- A ces, are represented. in said display as well as rier Ebeing coupled tQ an angul rly movable another objects. such as moving or" stationary airtenna 4; by gearing represented by the broken craft, and dimculty may be encountered in readily lines 5,. where y a the ant nna 4' i r ed 03' identifying those parts ofv the display which repmoved singularly under the actionv of. a driving resent the non-fixedobjects. particularly if the motor 5. carrier is moved in synchronism with fixed objects are large. or numerous. the antenna so. that the radial trace produced The: object oi the invention is'to provide. appaon the tube screen by the deflection of the beam ratus of'thetypereferredto whereby the efiect'of by coils 3 is causedto move angularly on said certain objects on the. display can be reduced. or screen. The signals received by antenna 4 by reeu in t d, fiection from objects in the field scanned by the According to the invention, radio location apantenna are applied to, the control electrode of paratus is provided incorporating an angularly tube l, thereby modulatingthe cathode ray beam movable antenna for receiving signals reflected to: produce. a display indicating. the positions of from objects inthe field explored by said antenna, said objects. Figure Z'r presents-the i pl y by a plan position indicator responsive to said sig- Way of example, objects in the explored field benals for providing a display indicating the posiins r p esented by bri h marks 7 and 8 On an tion f s id bje ts, a m terial representation to otherwise dark background. It will be assumed indicating selected objects only in said field, that the marks 7 represent fixed objects and that means for producing signals representative of the marks 8 represent moving or movable Objectssaid selected objects and means for causing said n Order to r m v t e m r 7 p y msignals representative of said selected objects to p t ly from the pre ta a transparency 9 vary the magnitude of signals representing said is prepared, having opaque areas It correspondselected objects as received by said antenna, ing to the marks 1, i. e., it represents the presenthereby to difierentiate on said plan position t t On Which Would b p u if y the indicator representations of said selected objects j s Co sp nd ng to m r s 7 W re present in from representations of other objects. h xplored fi ld- Tr n p n y 9 m y f r X- The signals produced from said material repreample be prepared by a photographic process sentation may, for example, be obtained by optifrom a suitable displ y exhibited by the P. P. I. cally scanning a transparency in which those pp tu or xample the displ exhibited areas which correspond to said selected objects When only the fixed'objects are in the explored are opaque and other areas are clear whereby the field. The transparency 9 is mounted close to or scanning apparatus produces an output which on the screen of a second cathode ray tube 29, varies in accordance with the opaqueness or Figure 1, the be m of Wh c i a d 3 p otransparency of the scanned areas. duce an angularly moving radial trace under In order that the said invention may be clearly the action of deflection coils I I mounted on a carunderstood and readily carried into effect, the I2 whic is m ved a gula ly throu h the same will now be more fully described with refint rmediary of searing 5 coupling carrier l2 erence to the accompanying drawing, in which: h the dr v n moto 6. that the screen of Figure 1 is a diagrammatic representation of tube 26 is scanned in synchronism with the scanapparatus according to the invention applied to Ring of the screen of tube l. The beam of tube apparatus of the type known as a plan position 20 is not modulated, so that the beam produces i di t r 1,) of) a moving light spot of constant brightness on the screen of tube 20. Light from said spot passes through transparent parts of transparency 9 and is focussed by an optical device l3 on to the cathode of a photo-electric tube M. The light from said spot is however cut off by the opaque areas of transparency 9. As the spot moves over the screen of tube 20 a voltage is generated by tube [4 which depends on the light reaching said device and which accordingly is substantially constant during the scanning of the parts of the tube screen adjacent transparent parts of the trans parency but which drops to zero when parts of the tube screen adjacent opaque areas of transparency 9 are being scanned. The output of tube M, which thus comprises negatively directed signals, is applied to an amplifier IS, the output from which is applied to the control electrode of tube l in such sense that said signals oppose the sig nals produced by reflection from the fixed objects in the explored field, so that said objects are not visible in the display on the screen of tube I or are less visible than they would otherwise be. Objects within the field explored by the radar apparatus and not represented on transpareney 9 will continue to be represented on the m P. P. I. screen, as shown by Figure 4, wherein only the marks 8 appear, the marks I of Figure 2 having been suppressed by the use of the transparency 9.

It will be appreciated that if only those objects are in the field explored which were in said field when said transparency was made, the P. P. 1. screen will give no'display. If however a corresponding object then enters the field, an area of the screen will be illuminated. Said illumination of the screen may be utilised to operate lightsensitive means whereby an audible or other warning is given when an object enters the explored field. Such an arrangement may for example be employed for giving warning of unauthorised persons entering an area, for example the perimeter of an airfield.

This application of the invention is shown in Figure 1, in which they light from the screen of tube 1 is arranged to be focussed by optical means represented at 16 on to the cathode of a photoelectric tube ll connected to an electric hell it, so that the bell is operated whenever said screen is illuminated What I claim is:

1. Radiolocation apparatus incorporating an angularly movable antenna for receiving signals reflected from objects in the field explored by said antenna, a first cathode ray tube, means for defiecting the beam of said tube to scan the screen of said tube, means responsive to said signals for modulating said beam to provide a display representing the positions of said objects, a second cathode ray tube, means for deflecting the beam of said second tube in synchronism with the beam of said first tube to produce a moving light spot on the screen of said second tube, a material representation indicating selected objects only in said field and disposed to be scanned by said light spot, a photoelectric device disposed for exposure to light from said material representation to generate signals corresponding to said selected objects, and means responsive to said last-mentioned signals for varying the amplitude of signals corresponding to said selected objects received by said antenna to differentiate in said display representations of said selected objects from representations of other objects.

2. Radiolocation apparatus according to claim 1, said representation having areas representing said selected objects and of different opacity from the remainder of said representation.

GEOFFREY WALTER HART.

Great Britain Nov. 28, 1949 

